Its not letting me quote you but 7 acc will give you +3.5% acc at 35% hit rate its a 10% increase in melee damage and ws frequency at 70% its 5% melee increase in damage and ws frequency. Not that youd ever be at 35% acc but its to help you understand its worth goes down closer to capped acc but even at high acc 90% adding 3.5% is a about a 3.9% increase in melee damage and ws frequency. (90 x .39 = 3.51)
The +2% double attack on the other hand is only a 2% increase in melee damage and ws frequency.
So of course the only way the double attack can win is if you are over 93% acc which is very unlikely for 1 handers.
Btw 2 acc = roughly +1% hit rate source from wiki hit rate page: its been tested and prooven so you dont need to take my word for it quote:
" * When attacker's total accuracy is the same as the defender's total evasion, then the expected hit-rate is 75%
if Accuracy == Evasion → Hit-rate = 75%
* For every 1 increment of attacker's accuracy, attacker's expected hit-rate is raised by 0.5% "
Hit Rate